1. Field of the Invention
An aspect of the present invention relates to an electronic device, and more particularly, to an electronic device wherein a path of power supplied to display is switched according to whether external power is supplied.
2. Description of the Related Art
Electronic devices employing batteries are widely used to enable portability and mobility. Such electronic devices include portable computers like laptop computers, notebook computers, personal digital assistants (PDA); mobile phones; CD players; video camcorders; etc. Generally, the electronic devices are provided with a connection terminal for connecting an adapter to use external power through an AC/DC adapter, as well as a battery. A secondary battery which is rechargeable is employed in the electronic devices and is recharged by power from the adapter.
The electronic devices may be provided with a display panel to display an image thereon, and a liquid crystal display (LCD) panel is widely used as the display panel.
The LCD panel is a light-receiving display panel unlike a cathode ray tube (CRT) or a plasma display panel (PDP), and includes a lamp to provide light.
FIG. 1 illustrates an example of a power supply system of a conventional portable computer. As shown in FIG. 1, the portable computer includes an adapter 110 and a battery 111 to supply power; a battery charger 112 to charge the battery 111 by using power from the adapter 110; an adapter detector 113 to detect whether the adapter 110 is connected; an LCD panel 116; a lamp 115 to emit light to the LCD panel 116; an inverter 114 to receive power from the adapter 110 or the battery 111 and convert the power into alternating current power for driving the lamp 115; and a system power supply 120a to convert the power from the adapter 110 or the battery 111 into power for driving a system part 117.
The power from the adapter 110 or the battery 111 is supplied to the system power supply 120a and the inverter 114 according to switching movement of a VDC switch 118 in response to the detection of the adapter detector 113. The adapter detector 113 and the VDC switch 118 control the power supplied from the adapter 110 to be supplied to the system power supply 120a and/or the inverter 114, prior to the power supplied from the battery 111.
The system power supply 120a converts the power supplied from the adapter 110 or the battery 111 into power for driving the system part 117 to supply the converted power to each of electronic components of the system part 117. The system power supply 120a includes DC/DC converters 121a and 122a, e.g., a switching voltage regulator, to output power at different voltage levels. An inverter switch 137 is provided to cut off power supplied to the inverter 114.
In the power supply system shown in FIG. 1, a voltage level of the power input to the inverter 114 ranges from a voltage level of power output from the adapter 110 to a voltage level output by the battery 111. For example, if the voltage level of output power of the battery 111 is 9V to 11.1 V (for a 3S battery) and the voltage level of the output power of the adapter 110 is 19V, the voltage level of the input power of the inverter 114 ranges from 9V to 19V.
The inverter 114 is designed to have a breakdown voltage corresponding to 19V to satisfy the input voltage of 9V to 19V and duty fluctuation becomes large, thereby preventing a realization of high efficiency in selecting a MOSFET as a switching element and in designing a high voltage transformer.
FIG. 2 illustrates another example of a power supply system of another conventional portable computer. Unlike the power supply system of the portable computer shown in FIG. 1, the power supply of the portable computer shown in FIG. 2 supplies the inverter 114 with power from one of DC/DC converters 121b and 122b of a system power supply 120b, thereby maintaining a voltage level of power input to the inverter 114, for example, at 5V.
However, while the battery 111 supplies power, in the power supply system of the portable computer shown in FIG. 2, the power from the battery 111 is input to the inverter 114 through the DC/DC converter 122b of the system power supply 120b and goes through a power conversion process twice, thereby lowering conversion efficiency of the DC/DC converter 122b and the inverter 114 corresponding to load in view of the battery 111, and thus losing electric power unnecessarily. That is, the conversion efficiency of the DC/DC converter 122b and the inverter 114 should be more than 95%, respectively, to maintain the conversion efficiency of the load of more than 90% with respect to the input to the battery 111. However, it is difficult to realize the DC/DC converter 122b and the inverter 114 with more than the 95% conversion efficiency.